Family Pedigrees/Sex Determination

• What is cystic fibrosis (CF) caused by?

  A recessive allele
• How can pedigree analysis be used in genetics?

  To study the inheritance of dominant and recessive alleles
• What is the purpose of a family pedigree?

  • Show inheritance of a genetic condition within a family
  • Predict the chance of inheriting a faulty allele
• What evidence supports that PTC tasting is controlled by a dominant allele?

  Individuals 1 and 2 are tasters, but their children are non-tasters
• What is the genotype of individual 2 in the PTC tasting example?

  It is heterozygous (Tt)
• What is the probability that the fifth child of individuals 9 and 10 will be a PTC taster?

  50% or 1/2
• How can you calculate the probability of Gill and Harry having a child with cystic fibrosis?

  Using a Punnett square
• What is the probability of having a child with cystic fibrosis if both parents are carriers?

  25% or 1/4
• What is the significance of dominant and recessive alleles in traits?

  • Dominant alleles require only one copy to express the trait
  • Recessive alleles require two copies to express the trait
• How is the sex of humans determined?

  At fertilisation
• What are the sex chromosomes for females and males?

  Females have XX and males have XY
• What is the difference between genotype and phenotype?

  Genotype is the genetic makeup, while phenotype is the observable traits
• Why are gametes considered haploid?

  Because they are produced by meiosis
• What do all of a woman's gametes contain in terms of sex chromosomes?

  All contain one X chromosome
• What is the composition of a man's gametes regarding sex chromosomes?

  50% contain one X chromosome and 50% contain one Y chromosome
• How do genetic diagrams and Punnett squares help in genetics?

  • Show inheritance patterns
  • Predict probabilities of traits in offspring
• At what stage is the sex of a baby determined?

  When the egg is fertilised
• What is the chance of a couple with two sons having a girl?

  50% or 1/2
• Why do human egg cells all contain one X chromosome?

  Because they are produced by meiosis